The present invention is an apparatus and process for determining the amount of condensable water in a vapor.
Moisture measurements are critical in a great variety of processes, and there are many techniques for measuring the moisture content in vapor. Popular techniques include spectroscopy and dew point sensors which sense a change in electrical capacitance due to condensation on the surface of a probe; see U.S. Pat. No. 5,123,277, U.S. Pat. No. 5,332,901, U.S. Pat. No. 5,357,441, and EP 0409546A2. However, measuring moisture in a vapor atmosphere becomes much more challenging when that atmosphere is at extremely high temperatures such as from 250xc2x0 C. to 1000xc2x0 C. At these extreme temperatures, capacitance probes and spectroscopic probes or flow cells fail. An Environmental Protection Agency method resorts to taking a portion of the vapor atmosphere and condensing any water present in the vapor; see 40 C.F.R. 60, App. A, Meth. 4. The amount of water condensed is either weighed or read volumetrically. Measurements by condensing and weighing or reading volumetrically require a significant sample size which may take an extensive period of time to collect. Also, manual weight or volumetric readings lack precision due to the subjectivity of the manual readings.
The present invention provides a technique and apparatus for making moisture measurements of a vapor phase which eliminate the subjectivity of the manual techniques and that may be applied in high temperature applications. The unique design of the apparatus allows for accurate precise moisture measurements on a small sample size and the method of making those measurements provides steps for minimizing error. Furthermore, the small sample size allows for rapid determinations and the application of capacitance measurements as an analytical tool serves to eliminate subjectivity.
The purpose of the invention is to provide a process and apparatus for measuring the amount of condensable water in a vapor. The preferred apparatus is a small volume vessel having a cooled condenser arm and a cooled collection chamber and is further equipped with a capacitance probe having a length extending into the collection chamber of the vessel. The process begins with calibrating the apparatus and then adjusting the level of water in the collection chamber of a vessel so that from about 5 to about 15 percent of the length of the capacitance probe is immersed in the water and measuring and recording an initial capacitance, CI. A measured amount of vapor is passed through the vessel in an amount sufficient to condense water into the collection chamber of the vessel. The vessel is purged with dry air for only such time as necessary to flush any droplets of water retained in the condenser arm of the vessel into the collection chamber of the vessel. A final capacitance, CF, is measured and recorded. The change in capacitance is calculated, xcex94C=(CFxe2x88x92CI), and the difference, xcex94C, is usedalong with the calibration to determine the amount of water condensed. With the amount of water condensed and the measured amount of vapor passed through the vessel, the amount of water in the vapor may be readily calculated. The collection chamber of the vessel may be drained and purged to remove all water in preparation of another analysis. The steps may be repeated, with the calibration step only repeated periodically or as needed.